The effect of vitamin concentrates on the flavor of pasteurized fluid milk

Fluid milk consumption in the United States continues to decline. As a result, the level of dietary vitamin D provided by fluid milk in the United States diet has also declined. Undesirable flavor(s)/off flavor(s) in fluid milk can negatively affect milk consumption and consumer product acceptability. The objectives of this study were to identify aroma-active compounds in vitamin concentrates used to fortify fluid milk, and to determine the influence of vitamin A and D fortification on the flavor of milk. The aroma profiles of 14 commercial vitamin concentrates (vitamins A and D), in both oil-soluble and water-dispersible forms, were evaluated by sensory and instrumental volatile compound analyses. Orthonasal thresholds were determined for 8 key aroma-active compounds in skim and whole milk. Six representative vitamin concentrates were selected to fortify skim and 2% fat pasteurized milks (vitamin A at 1,500–3,000 IU/qt, vitamin D at 200–1,200 IU/qt, vitamin A and D at 1,000/200–6,000/1,200 IU/qt). Pasteurized milks were evaluated by sensory and instrumental volatile compound analyses and by consumers. Fat content, vitamin content, and fat globule particle size were also determined. The entire experiment was done in duplicate. Water-dispersible vitamin concentrates had overall higher aroma intensities and more detected aroma-active compounds than oil-soluble vitamin concentrates. Trained panelists and consumers were able to detect flavor differences between skim milks fortified with water-dispersible vitamin A or vitamin A and D, and unfortified skim milks. Consumers were unable to detect flavor differences in oil-soluble fortified milks, but trained panelists documented a faint carrot flavor in oil-soluble fortified skim milks at higher vitamin A concentrations (3,000–6,000 IU). No differences were detected in skim milks fortified with vitamin D, and no differences were detected in any 2% milk. These results demonstrate that vitamin concentrates may contribute to off flavor(s) in fluid milk, especially in skim milk fortified with water-dispersible vitamin concentrates.     

A survey of vitamin A and D contents of fortified fluid milk in Ontario

High performance liquid chromatographic methods for measuring the concentration of vitamins A and D in fluid milk were validated and used to assess the level of these nutrients in Ontario retail milk samples. Thirteen and fifteen fortified milk samples were tested for vitamins A and D, respectively. Repeatability relative standard deviation values for vitamins A and D in milk were generally less than 10%. Recoveries varied from 87 to 107%. Vitamin D results indicated that only 20% of skim, 40% of 2% fat milk, and 20% of whole milk contained the recommended levels, whereas 46% of skim, and 77% of 2% fat milk had the required levels of vitamin A. The results indicate that vitamin level varies widely in Ontario retail milk.     

Evaluation of increased vitamin D fortification in high-temperature, short-time-processed 2% milk, UHT-processed 2% fat chocolate milk, and low-fat strawberry yogurt

The objective of this study was to determine the effect of increased vitamin D fortification (250 IU/serving) of high-temperature, short-time (HTST)-processed 2% fat milk, UHT-processed 2% fat chocolate milk, and low-fat strawberry yogurt on the sensory characteristics and stability of vitamin D during processing and storage. Three replicates of HTST pasteurized 2% fat milk, UHT pasteurized 2% fat chocolate milk, and low-fat strawberry yogurt were manufactured. Each of the 3 replicates for all products contained a control (no vitamin D fortification), a treatment group with 100 IU vitamin D/serving (current level of vitamin D fortification), and a treatment group with 250 IU vitamin D/serving. A cold-water dispersible vitamin D₃ concentrate was used for all fortifications. The HTST-processed 2% fat milk was stored for 21 d, with vitamin D analysis done before processing and on d 0, 14, and 21. Sensory analysis was conducted on d 14. The UHT-processed 2% fat chocolate milk was stored for 60 d, with vitamin D analysis done before processing and on d 0, 40, and 60. Sensory analysis was conducted on d 40. Low-fat strawberry yogurt was stored for 42 d, with vitamin D analysis done before processing, and on d 0, 28, and 42. Sensory analysis was conducted on d 28. Vitamin D levels in the fortified products were found to be similar to the target levels of fortification (100 and 250 IU vitamin D per serving) for all products, indicating no loss of vitamin D during processing. Vitamin D was also found to be stable over the shelf life of each product. Increasing the fortification of vitamin D from 100 to 250 IU/serving did not result in a change in the sensory characteristics of HTST-processed 2% fat milk, UHT-processed 2% fat chocolate milk, or low-fat strawberry yogurt. These results indicate that it is feasible to increase vitamin D fortification from 100 to 250 IU per serving in these products.     

Effect of Carrier Type and Amount on Vitamin A Light Degradation in Fortified Lowfat and Skim Milks

Effects of type and amount of retinyl palmitate carrier on light stability of all-trans retinyl palmitate in fortified lowfat milks were investigated. Skim and 2% fat milks were fortified with retinyl palmitate using butter, coconut, corn, or peanut oil as the vitamin carrier. After pasteurization and homogenization, fortified milk samples were exposed to light in glass tubes. At regular intervals, samples were removed from light and analyzed for all-trans retinyl palmitate using high performance liquid chromatography. Less light-induced loss of all-trans retinyl palmitate occurred in skim and 2% fat milks fortified using butter or coconut oil than those using corn or peanut oil. Amount of coconut or corn oil used to incorporate retinyl palmitate also played a role in its light-induced degradation rate. At a carrier concentration of .001% (vol/vol) in skim milk, light degradation of all-trans retinyl palmitate proceeded approximately twice as fast as .01 or .1% (vol/vol). Addition of Tween 80 as an emulsifier had negligible effect on retinyl palmitate light degradation in fortified skim milk.     

Vitamin Fortification of Fluid Milk

Vitamin concentrates with vitamins A and D are used for fortification of fluid milk. Although many of the degradation components of vitamins A and D have an important role in flavor/fragrance applications, they may also be source(s) of off‐flavor(s) in vitamin fortified milk due to their heat, oxygen, and the light sensitivity. It is very important for the dairy industry to understand how vitamin concentrates can impact flavor and flavor stability of fluid milk. Currently, little research on vitamin degradation products can be found with respect to flavor contributions. In this review, the history, regulations, processing, and storage stability of vitamins in fluid milk are addressed along with some hypotheses for the role of vitamin A and D fortification on flavor and stability of fluid milk.     

Vitamin D content and variability in fluid milks from a US Department of Agriculture nationwide sampling to update values in the National Nutrient Database for Standard Reference

This study determined the vitamin D₃ content and variability of retail milk in the United States having a declared fortification level of 400 IU (10 μg) per quart (qt; 1 qt = 946.4 mL), which is 25% daily value per 8 fluid ounce (236.6 mL) serving. In 2007, vitamin D₃ fortified milk (skim, 1%, 2%, whole, and 1% fat chocolate milk) was collected from 24 statistically selected supermarkets in the United States. Additionally, 2% milk samples from an earlier 2001 USDA nationwide collection were reanalyzed. Vitamin D₃ was determined using a specifically validated method involving HPLC with UV spectroscopic detection and vitamin D₂ as an internal standard. Quality control materials were analyzed with the samples. Of the 120 milk samples procured in 2007, 49% had vitamin D₃ within 100 to 125% of 400 IU (10 μg)/qt (label value), 28% had 501 to 600 IU (12.5-15 μg)/qt, 16% had a level below the label amount, and 7% had greater than 600 IU (15 μg)/qt (>150% of label). Even though the mean vitamin D₃ content did not differ statistically between milk types, a wide range in values was found among individual samples, from nondetectable [<20 IU (0.5 μg)/qt] for one sample to almost 800 IU (20 μg)/qt, with a trend toward more samples of whole milk having greater than 150% of the labeled content. On average, vitamin D₃ in 2% milk was higher in 2007 compared with in 2001 [473 vs. 426 IU (11.8 vs. 10.6 μg)/qt].     

Influence of milk fat, milk solids, and light intensity on the light stability of vitamin A and riboflavin in lowfat milk

Retinyl palmitate and riboflavin were quantified in milk samples exposed to fluorescent light. Effects of compositional factors were determined by comparing rates of loss of riboflavin and vitamin A in milks with different amounts of milk fat and milk solids. Upon exposure to fluorescent light, rates of vitamin A and riboflavin loss were lower in whole milk than in skim milk. Riboflavin degraded more slowly in skim milk with 1% added nonfat dry milk than in skim milk with no added solids. No additional protective effect for riboflavin was found when added solids were increased from 1 to 3%. Compared with milk with no added solids, 1% added nonfat dry milk did not increased protection for vitamin A, but a protective effect was noted when the skim milk was fortified with 3% nonfat dry milk. Increasing light intensity increased the rates of loss of both vitamins, and riboflavin was lost at a greater rate.     

Effect of Milk Fat on the Stability of Vitamin A in Ultra-High Temperature Milk

The stability of vitamin A in ultra-high temperature milks with .15, 2.92, 6.16, and 9.7% fat during storage at 26°C was studied over 3 wk. Milks were fortified with synthetic retinyl palmitate to a final concentration of approximately 120 μg retinol equivalent/I 00 ml milk. The four milk samples were ultra-high temperature processed and packaged in 100 ml sterile milk dilution bottles and stored in the dark at 26°C for 3 wk. Vitamin A concentrations decreased rapidly during the first 2 wk of storage then stabilized. Degradation rates during the first 2 wk were linear and varied inversely with the fat content in the milk (the more fat, the slower the rate of degradation). Final vitamin A concentrations at the end of 3 wk of storage were higher in milk with high fat and closely corresponded to the native vitamin A concentrations present in milk prior to fortification. The results indicate a possible protective effect due to fat or a difference in stability between native and synthetic vitamin A.     

Impact of fortification with iron salts and vitamin A on the physicochemical properties of laboratory‐pasteurised toned milk and bioaccessibility of the added nutrients

The sensory and physicochemical attributes of pasteurised milk fortified with soluble ferric pyrophosphate (FPP) (25 mg/L iron) and vitamin A (2500 IU) were comparable to unfortified control samples. The heat coagulation time (HCT) of fortified milks was comparable to the control and exhibited a type A curve with HCT–pH maxima at the acidic side of the natural pH. The distribution pattern of iron in different milk fractions was similar in control and fortified milk samples. The bioaccessibility of iron, estimated through in vitro digestibility of milk fortified with vitamin A and iron, was found to be slightly higher than that of milk fortified with iron alone.     

Short communication: Comparison of 3 rapid methods for analysis of vitamin degradation compounds in fluid skim milk

Vitamin fortification of dairy products, including fluid milk and fortified whey protein beverages, is an industry standard but can lead to the development of off-flavor compounds that are difficult to extract and detect by instrumental methods. Previous work has identified these compounds and their specific role in off-flavors in skim milk, but efficient extraction and quantification of these compounds remains a challenge. Three rapid methods (stir bar sorptive extraction, solvent-assisted stir bar sorptive extraction, and solid-phase microextraction) were compared for their ability to effectively recover vitamin degradation volatiles from fluid skim milk. The performance of the 3 methods for detecting and quantifying vitamin degradation-related volatile compounds was determined by linear regression of standard curves prepared from spiked standards of 5 vitamin degradation volatiles, the reproducibility on the same day and between days as measured by the average relative standard deviation of each standard curve, and the limits of detection and quantitation. Measurement of vitamin degradation compounds in commercial pasteurized fortified skim milks was also conducted using each method. Detection of selected vitamin degradation volatiles was linear in skim milk (0.005–200 μg/kg). Coefficient of determination values differed between methods and compounds. Within-day and between-day percentage of relative standard deviation also varied with compound and method. Limits of detection and quantitation values for all methods except solid-phase microextraction were lower than concentrations of selected volatile compounds typically found in commercial milk. Solvent-assisted stir bar sorptive extraction with a 10-mL sample volume provided the most consistent detection of selected compounds in commercial milks. Based on linearity, relative standard deviation, and limits of detection and quantitation, cyclohexane solvent-assisted stir bar sorptive extraction with 10-mL sample volume is recommended for the quantitation of vitamin degradation-related volatiles in fluid skim milk.     

Effect of fat content on sensory and physico‐chemical properties of laboratory‐pasteurised calcium‐ and vitamin D‐fortified mixture of cow and buffalo milk

The influence of milk fat on physico‐chemical properties of calcium and vitamin D‐fortified milk was investigated. Sensory scores, curd tension, viscosity, rennet coagulation time and TBA value increased with the increase in fat content. Calcium and vitamin D fortification had no effect on sensory scores, whereas a significant increase was observed in curd tension and viscosity. The TBA value of fortified milk was significantly lower than that of the unfortified milk. The rennet coagulation time of milk increased significantly with addition of calcium phosphate, whereas calcium citrate fortification had no significant effect. All milk samples were stable to alcohol.     

Characteristics of reduced fat milks as influenced by the incorporation of folic acid

Folic acid plays an important role in the prevention of neural tube defects (e.g., spina bifida and anencephaly), heart defects, facial clefts, urinary abnormalities, and limb deficiencies. Milk and milk products serve as a potential source for folic acid fortification because of the presence of folate-binding proteins that seem to be involved in folate bioavailability. Although milk is not a good source of folic acid, fortification could help in the prevention of the above-mentioned defects. The objective of this study was to examine the physicochemical characteristics of reduced fat milks fortified with folic acid. Reduced fat milks were prepared using 25, 50, 75, and 100% of the recommended dietary allowance of 400 μg of folic acid. Treatments included addition of folic acid at these levels before and after pasteurization. Color, pH, fat, protein, viscosity, folic acid concentration, folate-binding protein concentration, folate-binding protein profile, standard plate count, and coliform counts were determined on d 1, 7, 14, and 21. A consumer acceptability test was conducted on d 7. Data from the consumer panel were analyzed using ANOVA (PROC GLM) with means separation to determine the differences among treatments. Data obtained from the color, pH, fat, protein, viscosity, folic acid concentration, folate-binding protein concentration, standard plate count, and coliform counts were analyzed using the GLM with a repeated measure in time. Significant differences were determined at P < 0.05 using Tukey's Studentized Range Test. There were no differences in the electrophoretic mobility of folate-binding protein in the samples. The concentration of folic acid was significantly higher in reduced fat milks fortified with folic acid after pasteurization compared with the treatments in which folic acid was added before pasteurization. The consumer panelists did not find any significant differences in flavor, appearance, or texture of folic acid fortified reduced fat milks compared with that of the control. Fortification of reduced fat milks with folic acid can be accomplished without adversely affecting the product characteristics.     

Effect of emulsifiers and fortification methods on light stability of vitamin A in milk

Lowfat milk is commercially fortified during processing by adding small quantities of oil containing an emulsifier and vitamin A. Added vitamin A is degraded more rapidly than indigenous vitamin A when milk is exposed to light. The objective of this research was to determine if added vitamin A could be made as stable to light as naturally occurring vitamin A by placing it in the more dilute milk fat environment with naturally occurring emulsifiers. Using HPLC to quantify retinyl palmitate, the effect of emulsifiers indigenous to milk versus a commercial emulsifier was first investigated. Butter serum, rich in fat globule membrane material, was compared with Durfax 80 in a 1% recombined milk system. No difference was found in vitamin A stability to light due to emulsifier type. A second experiment on 1% milk compared light stability of vitamin A added in concentrated milk fat emulsion, vitamin A added to all the milk fat, and indigenous vitamin A. Indigenous vitamin A and vitamin A added to all the fat were equally stable and more stable than vitamin A added in a concentrated milk fat emulsion.     

A comparison of the composition, coagulation characteristics and cheesemaking capacity of milk from Friesian and Jersey dairy cows

Twenty-nine multiparous cows of each of the Jersey and Friesian breeds, all kappa-casein AB phenotype, were grazed together and managed identically. On three occasions during 10 d in spring (early lactation), milk was collected from all cows at four consecutive milkings and bulked according to breed. On a separate occasion, milk samples were also collected from each cow at consecutive a.m. and p.m. milkings to form one daily sample per cow. The bulked milks (800-1000 l per breed on each occasion) were standardized to a protein:fat (P:F) ratio of 0.80, and 350 l from each breed was made into Cheddar cheese. The solids content of the remaining Friesian milk was then increased by ultrafiltration to a solids concentration equal to that of the Jersey milk. This solids-standardized Friesian milk and a replicate batch of P:F standardized Jersey milk were made into two further batches of Cheddar cheese in 350-l vats. Compared with Friesian milk, Jersey milk had higher concentrations of most milk components measured, including protein, casein and fat. There were few difference in milk protein composition between breeds, but there were differences in fat composition. Friesian milk fat had more conjugated linoleic acid (CLA) than Jersey milk fat. Jersey milk coagulated faster and formed firmer curd than Friesian milk. Concentrations of some milk components were correlated with coagulation parameters, but relationships did not allow prediction of cheesemaking potential. Jersey milk yielded 10% more cheese per kg than Friesian milk using P:F standardized milk, but for milks with the same solids concentration there were no differences in cheese yield. No differences in cheese composition between breeds were detected. Differences in cheesemaking properties of milk from Jerseys and Friesians were entirely related to the concentrations of solids in the original milk.     

Comprehensive survey of pasteurized fluid milk produced in the United States reveals a low prevalence of Listeria monocytogenes

A comprehensive survey was undertaken to generate contemporary data on the prevalence of Listeria monocytogenes in pasteurized fluid milk produced in the United States. Samples (5,519) near the sell-by expiration date were purchased at retail outlets over a 5-week period and analyzed for presence of L. monocytogenes. Products consisted of whole milk, nonfat milk, and chocolate milk packaged in gallon, half gallon, quart, pint, and half-pint containers. Samples were collected from both large and small retail stores in urban and suburban locations in four FoodNet cities (Baltimore, Md., Atlanta, Ga., St. Paul/ Minneapolis, Minn., and San Francisco, Calif.). Samples were prescreened for L. monocytogenes by the AOAC-approved rapid Vitek immunodiagnostic assay system, enzyme-linked fluorescent assay method. Positive prescreening samples were cultured according to the Bacteriological Analytical Manual, enumerated for L. monocytogenes with a nine-tube most-probable-number (MPN) procedure, and confirmed by biochemical characterization. The frequency of isolation of L. monocytogenes in these products was 0% (0 of 1,897) in whole milk, 0.05% (1 of 1,846) in nonfat milk, 0% (0 of 1,669) in chocolate milk, and 0% (0 of 107) in other (reduced fat and low fat) milk samples. Overall, L. monocytogenes was confirmed in only 0.018% of pasteurized milk samples (1 of 5,519). Enumeration of the single confirmed positive nonfat milk sample revealed low-level contamination (<0.3 MPN/g), even when sampled 5 days past the expiration of the sell-by date. The results confirm the low frequency of contamination of pasteurized fluid milk products by L. monocytogenes for products sold in the United States and reaffirm the reduction of contamination frequency of fluid milk by L. monocytogenes when compared with earlier estimates from the U.S. Food and Drug Administration Dairy Safety Initiatives Program.     

SFC-Q-TOF-MS法鉴定4 种家畜乳甘油三酯及特征分析

对家畜乳尤其是特种家畜乳脂肪甘油三酯（triacylglycerols，TAGs）进行系统鉴定和研究。采集荷斯坦牛、山羊、蒙古马和双峰驼原奶样品31 份，用超临界流体色谱-四极杆飞行时间质谱（supercritical fluid chromatography-quadruple time-of-flight mass spectrometry，SFC-Q-TOF-MS）检测鉴定TAGs组成，并进行主成分分析（principal component analysis，PCA）。结果表明：4?种家畜乳共鉴定出145?种TAGs，相对分子质量为470～888，酰基链总碳数为24～54，双键数为0～9；由14?种碳数4～20、双键数0～3的脂肪酸构成。牛、山羊、马和骆驼乳分别鉴定出60、66、74?种和44?种TAGs。马、骆驼、牛和山羊乳不饱和TAGs相对含量依次为82.2%、61.1%、51.7%和43.8%；马乳含亚麻酸的TAGs高达45.43%；骆驼乳TAGs脂肪酸组成最简单，至少含肉豆蔻酸、棕榈酸、硬脂酸和油酸中的一种；驼乳脂肪O-P-O相对含量最高，为5.04%，山羊乳脂肪最低，仅为1.8%；山羊乳主要TAGs都由饱和脂肪酸组成。4?种家畜乳的基峰色谱图差异明显，对TAGs进行PCA?4?种家畜乳样品以物种聚类明显分离，距离远近符合物种分类学，提示TAGs可建模判别家畜乳的物种。     

Effects of sterilization, packaging, and storage on vitamin C degradation, protein denaturation, and glycation in fortified milks

Monitoring the nutritional quality of dietetic milk throughout its shelf life is particularly important due to the high susceptibility of some vitamins to oxidation, and the continuous development of the Maillard reaction during storage.The objective of this paper was to evaluate the vitamin C content and protein modification by denaturation and glycation on fortified milk samples (growth milks) destined for 1- to 3-yr-old children. The influences of the sterilization process, formulation, packaging, and storage duration at ambient temperature in the dark were studied. Vitamin C degradation was particularly influenced by type of packaging. The use of a 3-layered opaque bottle was associated with complete oxidation of vitamin C after 1 mo of storage, whereas in the 6-layered opaque bottle, which has an oxygen barrier, the vitamin C content slowly decreased to reach 25% of the initial concentration after 4 mo of storage. However, no significant effect of vitamin C degradation during storage could be observed in terms of Maillard reaction, despite the fact that a probable impact occurred during sterilization. Furosine content and the FAST (fluorescence of advanced Maillard products and soluble tryptophan) index-indicators of the early and advanced Maillard reaction, respectively-were significantly higher in the in-bottle sterilized milk samples compared with UHT samples, and in fortified milk samples compared with cow milk. However, after 1 mo, the impact of storage was predominant, increasing the furosine level and the FAST index at similar levels for the differently processed samples. The early Maillard reaction developed continuously throughout the storage period.In conclusion, only packaging comprising an oxygen and light barrier is compatible with vitamin C fortification of milk. Furthermore, short storage time or low storage temperature is needed to retard vitamin C degradation, protein denaturation, and development of the Maillard reaction.     

Vitamin A degradation and light-oxidized flavor defects in milk

To determine the effects of light exposure on vitamin A degradation and on light-oxidized flavor development, samples of whole, reduced fat, and nonfat milk were exposed to fluorescent light (either 1000 or 2000 lx) at time intervals of 2, 4, 8, or 16 h. Measurable vitamin A losses occurred at 2, 4, and 16 h at 2000 lx for nonfat, reduced fat and whole milk, respectively. Moderate light-oxidized flavors were detected after 4 h of light exposure (2000 lx) in the whole and reduced fat milk and after 8 h in nonfat milk. The different types of milk show a significant difference in relative flavor scores. By 16 h at 2000 lx, relative light-oxidized flavor development was lower in nonfat milk than in whole or reduced fat milk. The presence of milk fat appears to protect against vitamin A degradation in fluid products, but adversely affects the flavor quality of milk after exposure to light. In summary, these findings demonstrate that even a brief, moderate light exposure (2 h; 2000 lx) can reduce the nutritional value and flavor quality of fluid milk products.     

Constituents of nutritional relevance in fermented milk products commercialised in Italy

Fermented milk products represent an increasing share of the dairy products consumed in Italy. The nutritional value of these products is related to the milk utilised and to the eventual presence of other ingredients (milk powder, sugar, fruit puree and fruit extracts), whereas the microrganisms used can affect texture and organoleptic characteristics. In this paper constituents of nutritional relevance such as protein, fat, total carbohydrate, amino acids, minerals, vitamin A, vitamin E and cholesterol, have been evaluated in yoghurts, fermented milks (plain and with essences) and Quark cheeses (plain and with fruits). This study confirms the high nutritional quality of fermented milks and stresses the role of non-milk ingredients in modifying and, sometimes, improving the dietary contribution of these products.